I think the term is is chine walk. I've experienced that on several models, my gpr did it around 18-20, consistently.
my RXT just did it to me last Sunday at around 15, as I was slowing down heading into a no wake zone.
Some will say its a good thing, it means the hull is trying to lift itself out of the water, its asking you for more power, like a racehorse,,, the ski wants to run.
it seemed to happen when the front of the hull where it went from the V to the flatter part was hitting the water just right.... The V will catch the water and just as it starts to pull the flatter part will catch and it settles back, then repeats.
bumping the trim down a bar or two sometimes does the trick, by raising or lowering the front of the hull you can usually manipulate the walk, but for me, it was just a reminder that I was going too slow, throttle always solved the problem. I would literally blip the throttle up a couple mph and it disappeared.
If you tend to speed up or slow down rather rapidly, you may never experience this once on your ski, so if I brap up from 5mph to 40 in a a couple seconds, nothing, but if I'm puttering about at that low rpm range i'll experience it.
Oddly enough more throttle solved my porpoising issues as well, I'm beginning to think that more rpm's is the solution to all of lifes problems !